Diesel engines have many moving parts that require lubrication. Engine durability is directly related to the ability of engine oil to lubricate the moving parts. However, the lubricating ability of the engine oil becomes degraded over time. Therefore, most manufacturers provide engine oil maintenance schedules to determine when the engine oil should be changed. The maintenance schedules are typically based on mileage although engine operating conditions directly relate to the degradation of engine oil. Thus, it is desirable to determine when the engine oil should be changed based on operating conditions of the engine.
In one method the degradation of engine oil is determined from monitoring engine revolutions, engine oil temperature, and soot accumulation in engine oil. However, during regeneration of a diesel particulate filter using a post injection strategy, fuel is accumulated in the engine oil. The accumulation of fuel degrades the ability of the engine oil to properly lubricate the engine. Therefore, it is desirable to determine when the engine oil should be changed due to the accumulation of fuel in the engine oil.